The river Housatonic appears to have made its way through this range, for the same rock continues on the western side of the river parallel to it in the mountains of Kent, Sharon, and Salisbury. In Litchfield commences a range of porphyritic granite, or _porphyritic gneiss_, which alternates with the common gneiss, and in some instances rests upon it. This rock begins at Mount Prospect, between Litchfield and Warren, and runs through South Farms, Bethlem, and Watertown. The crystals of feldspar in it, are often very perfect. The primitive granite, as a rock, is not found, though it lies scattered on the surface in great quantities, and large masses. The graphic granite in this region is often remarkably fine. Mica slate constitutes a considerable part of those rocks that rest on the gneiss, though never found in such elevated situations. The mica slate rocks are always inclined at a great angle with the horizon, and follow the direction of the other range. Litchfield village, Chesnut hill, and great part of Harwington, are entirely composed of this rock. The Bantum and the Waterbury rivers have their bottoms of it. Some of the brooks entering the Waterbury, have cut their passage through the mica slate, leaving walls of 40 or 50 feet on each side, traversed by veins of a very coarse-grained granite, and often much mixed with sulphuret of iron. The slate near Harwington meeting-house contains a great quantity of sulphuret of iron. Mica slate likewise lies on the sides of the gneiss range in Canaan and Salisbury, where it dips under the limestone. _Sienite_ is scattered on the surface in large masses, especially where the porphyritic gneiss is found. Sometimes, however, the masses are so large as to form mountains. Mount Tom, between Litchfield and Washington, is of this nature, being entirely composed of sienite, resting on gneiss. Slaty sienite is frequently found, having a very large proportion of hornblende. The minerals that are found in this region, are much more interesting than its geology. In describing them, I shall confine myself to the district east of the limestone range, intending at some future time to investigate and describe the limestone country. Carbonate of lime, the granular limestone, is scattered over the whole of this region. It often is found in the cavities of decayed quartz rocks, and contains tremolite and augite.